Fire alarm apparatus



Nov. 17, 1959 w. J. THORSEN 2,913,709

FIRE ALARM APPARATUS Filed May 10, 1957 Fig. I

Fig. 2

IN VEN TOR.

United States Patent I FIRE ALARM arranarus 7 Walter J. Thorsen, Cerrito, Application May 10,1957, Not 658,373

3 Claims. cram-221 This invention relates to a new type of closed circuit fire alarm system in which the circuit is-broken when a fire occurs. More specifically the system incorporates a method of utilizing closed circuit fire detectors in conjunction with one or more single' or'c'ompound thermalswitches which, in case of -a fire, act to intermittently actuate an alarm signalling device such as a bell, buzzer orthelike. gy Notwithstanding modern methodsof fire prevention,

fires cause almost one billion dollarfsf worthfd damage yearly. Much of this loss could be prevented bythe prompt discovery of these fires, which,-li ke cancer, if der controlbefore caught earlyenough can be brought' too much damage has occurred.

. highly reliable, inexpensive closed circuit fire detectors 2,913,709 PatentedNov. 17, 1959 are used.

A further objectis to provide a circuit for the fire detectors.

An additional object'isto incorporate one or more .single or compound thermal switches in the control" unit-such switches being practically indestructible and of extremely low cost.

Still another object is toprovide a special circuit for the above switch or switches such that a flashing,

alarm signal will result.

A further object is to providea control unit which utilizes the low voltage transformer and the doorbell already in existence in the building, thus greatly reducing material and installation costs. p I

A further object is' toprovide an alarm single loop closed 7' system which V is so simple to install that any do-it-yourselff person Manyfire warning systems are available, but all are too expensive for the average home owner, particularly because they necessitate the use of magnetic relays. Moreover the open circuit type of fire detector; which is used with most known systems, is often faulty in operation due to contactv contamination problems, and

requires an excessive amount of"wire A particular advantage of the system is that it utilizes thermal switches which'have excellent electrical characteristics and are low in'cost in comparisonwith magnetic relays. Another advantage. is that the invention utilizes a closed circuit system-which eliminates contact contamination problems and which will give a signal when the circuit isaccidentally opened orbroken. Also, the alarm system of this invention offers the advantage of a flashing or intermittent alarm signal, which I is more likely to awaken the occupant of a building than a steady signal as provided in known systems.

if this invention may installthe whole systemin an afternoon.

.Other objects of my invention will become apparent from a co nsideration of thejfollowing description, taken 7 in conjunction with" the attached drawings of which: "Figuresll and 2 are circuit diagrams of two embodi-,

ments of my invention.

"As illustrated in Figure 1 my first embodiment con sists of fire detectors 1 connected in a series loop circuit";

A by wires 2,. which are in turnconnected to control -'unit B, which in turn is connected to-existing dobrbellj C and existing power.source," transformer D. Fire l detectors are of conventional construction, including two conduction elements connected at their ends by a deposit ,of fusible metal.

In the event of a fire,- the. fusible I metal melts, breaking the; contact between the con- A further advantage of the present invention is that I existing bell or chime transformers can be used as a source of power and a separate power source as required with known alarm systems is eliminated.

I now havediscover'ed a new system of fire detection which incorporates inexpensive and reliable" closed circuit fire detectors mounted strategically in the areas desired to be protected, connected in a single, loop closed circuitto a control unit, in turn connected to an existing power transformer and an alarm signalling device. The control unit vcauses a small current to flow through this loop. When a fire occurs, the nearest fire detector opens the loop circuit and interrupts the current flowing through it. This actuates one or more single or compound thermal switches in the control unit in such a manner as to intermittently switch the alarm signallingdevice on,

ductors. Doorbell C 'rnay take the form of a conventional device of the type equipped with a closed circuit solenoid coil. Transformer D isja conventional bell transformer.

Transformer D 'is connected to hell C by wire Control unit B is connected to transformer D by wire}: and to hell C by wire 5. WireS is connected to wire'6 1 which is connected to contact point 7 and loop wire 2.

Wire 4 is connected to .wire 8 which is connected to one end of a low resistance heating coil 9 which is The. otherjend of wound around bimetal strip 10.

heating coil 9 is grounded to bimetal strip 10. Contact 11 is attached'to bimetal strip 10. One end of high? resistance heating coil 12 is also' grounded'to bimetal The operation of the system is as follows:

Transformer D impresses a voltage, via wire 3 bell C, across wires 4 and 5. The same voltage is therefore impressed across wires 6 and 8 incontrol unit B.

.strip 10 and its other end is attached 'to loop wire '2.

and:

.This causes a small current to flow through the'detector I loop wires 2 and detectors 1, high resistance coil 12, low I resistance coil 9, and wire 8. The total resistance of j coils 9 and 12 is sufficiently high thatthe current flow through bell C is too low tocause itto ring. However i the heat produced in coil 12 warms'bimetal'strip 10'; enough to flex it upwardly to maintain contacts 7 and 11 and off. When the fire is over and the, detector is tacts 7 and 11.

in the open position.

(In the absenceof heat strip 10 is biased downward to close contacts 7 and 11.) Yery little heatjs givenoff byv coil 9 because it has a low re-l;

sistance'in' comparison with coil 12.- I v When a fire occurs near afire detector 1' the current? flowing through the detector loop wiring 2 is interrupted.

This interrupts the flow of current through coils 9 and 12 and causes bimetal strip 10 to cool in a few seconds,,,,

thereby deflecting strip l0 downwarjdly and closing con- This causes. a heavy current to flowf through wire 3, bell C, wires5 and 6 fcontacts 7 and 11,.

a portion of bimetal strip 10, coil 9, and; wires 8 and 4,? thus causing the bell to ring. This jcurrent is now sufii} ciently heavy to cause appreciable heat'to be generated in coil 9. Bimetal strip 10 is thereby warmed up again in a few seconds, flexing upwardly and opening contacts 7 and 11. This interrupts the current flowing through bell B and stops it from ringing. Simultaneously the current flowing through-coil 9- is interrupted and thus bimetal strip 10 again cools in a few seconds, causing bell B to ring again, etc.- Thus an intermittent orflashing alarm signal is produced when a fire occurs near any fire de tector 1. When loop A, is again restored to its initial closedv condition, coil '12 again heats bimetal strip 10 sufliciently to maintain contacts 7 and 11 in the open position, terminating the alarm signals.

As illustrated in Figure 2 my second embodiment consists of fire. detectors 1 connected in a series loop circuit A by wires 2, which are in turn connected to control unit B, which is in turn connected to existing doorbell C and existing source of power, transformer D.

Transformer D is connected to. hell C by wire 3-. Control unit B is connected to transformer D by wire 4 and bell-C by wire 5. Wire isconnected to wire 13, in turn connected to bolt 14 which clamps bimetal strip 15 to insulating mount 16. Electrical contact is made between bolt 14 and bimetal strip 15. One end of resistance wire heating coil 17 is connected to bolt 14 and the other end to bolt 24. One end of. wire 19 is connected to bolt 14 and the other to one end of resistance wire coil 20. The other end of coil 20 is connected to wire 21 which is connected to loop wire 2. Contacts 26 and 22 are con- 24 which clamps bimetal strip 18 to insulating mount 16..

Electrical contact is made between bolt 24 and bimetal strip 18. Bolt 24 is connected to'wire 25, which is in turn connected to wire 25, which is in turn connected to wire 4. r

The operation of the system is as follows:

Transformer D impresses a voltage, via wire 3 and bell C, across wires 4 and 5 attached to control unit B. The same voltage is therefore impressed across wires 13 and 25 in control unit B. This causes a small current to flow through wire 13, bolt 14, wire 19, coil 20, wire 21, detector loop wiring 2 and detectors 1, wire 23, bolt 24, wire 25, and coil 17. The parallel resistance of coils 17 and 20 is high enough so'that the current flow through bell C is too low to cause it to ring. The heat produced in coils 17 and 20 warms up bimetal strips 15 and 18, causing them both to flex away from base 16, that is, downwardly and the contacts remain open. (In absence of any heat the contacts are likewise open.)

When a fire occurs near a fire detector 1 the current flowing through the detector loop wiring 2 is interrupted. This interrupts the flow of current through coil 20 and causes bimetal strip 18 to cool in a few seconds, thereby flexing strip 18 upwardly and closing contacts 22 and 26. This shorts out bolts 14 and 24 and causes bell C to ring. The shorting action simultaneously drops the voltage impressed across coil 17 to zero. Bimetal strip 15 cools in a few seconds, flexing upwardly and opens contacts 22 and 26. This causes bell C to stop ringing and simultaneously impresses the voltage across coil 17 again. The resulting heat causes contacts 22 and 26 to close again in a few seconds and bell C rings again etc. Thus, an intermittent or flashing alarm signal is produced when a fire occurs near any detector 1. When loop A is restored to its initial closed condition coil 20 again heats bimetal strip 18 sufliciently to maintain contacts 22 and 26 in the open position, terminating the alarm signals.

I claim as my invention:

1. A fire alarm system comprising a closed series circuit of a power source, an alarm unit, a loop containing at least one fire detector unit, a high resistance heating coil, and a low resistance heating coil, said coils being in heat-transfer relationship to a thermo-responsive arma ture, a pair of contacts, one contact connected to said alarm unit, the other contact being on said armature and connected through said armature and low resistance heating coil to said power source, said coils and armature being operative to maintain the contacts in open position under normal temperature conditions at which the circuit remains closed and in the event of unusual high temperature conditions which cause opening of a fire detector unit being operative to intermittently close said contacts whereby to intermittently connect said alarm unit directly to the power source to provide an intermittent alarm signal.

2. A fire alarm system comprising a closed series circuit of a power source, an alarm unit, a loop containing at least one fire detector unit, a high resistance heating coil, a low resistance heating coil, said coils being in heat-transfer relationship to a thermo-responsive annature, one end of said high resistance coil being connected to said loop, the other being connected to said armature, one end of said low resistance coil being connected to said armature, the other end being connected to said power source, a pair of contactors, one being connected said alarm unit, loop and coils in series, the series resistance of the coils being sufficient to prevent actuation of said alarm unit, the heat provided by said coils being suflicient to deflect the armature to maintain the contacts in open position, and in the event of unusual high temperature conditions which cause opening of a fire detector and subsequent disconnection of the coils from the source of power, cooling of the armature causing closing of the contacts whereby the alarm unit is connected to the power source through the low resistance coil, the subsequent heating of the armature by this coil causing opening of the contacts, the process of opening and closing of the contacts being intermittently repeated as long as the loop circuit remains open.

3. A fire alarm system comprising a closed series circuit of a power source, an alarm unit, a loop containing at least one detector unit and a first heating coil, said coil being in heat transfer relationship to a first thermo-responsive armature, said armature being connected to said power source and being provided with a contact, a second heating coil in parallel to said circuit one end connected to said power source the other to said alarm unit, said coil being in heat transfer relationship to a second thermoresponsive armature, said armature being connected to said alarm unit and being provided with a contact, said armatures being deflectable by heat in the same direction andbeing so positioned that when the loop circuit remains closed, as at normal temperatures, the heating effect of both coils deflect both armatures in the same direction maintaining the contacts in open position whereas when the loop circuit is opened, as at unusually high temperatures, current to the first coil is interrupted resulting in deflection of the first armature toward the second armature thus closing the contacts and connecting the alarm unit directly to the power source, and shortcirouiting the second coil which in turn causes cooling and deflection of the second armature away from the first, re-opening the contacts whereby a circuit from the power source to the alarm unit through the second coil is reestablished and the second coil again heats the second armature, deflecting it to close the contacts and to connect the alarm unit directly to the power source whereby to provide an intermittent alarm signal as long as the loop circuit is open.

References Cited in the file of this patent UNITED STATES PATENTS 

